The present invention relates to a method of displaying a color picture by using a liquid crystal device, particularly a picture display method using a liquid crystal device for effecting color picture display by illuminating a liquid crystal device sequentially with R (red), G (green) and B (blue) lights in synchronism with optical switching by the liquid crystal device so as to sequentially display picture of R, G and B respective colors.
Hitherto, color picture display has been practiced by using liquid crystal device according to methods including the following methods (1) and (2).
(1) A method of continuously illuminating a liquid crystal device equipped with a color filter with white light. Each pixel of the liquid crystal device corresponds to one color filter segment (one of R, G and B). The respective pixels are disposed in division in sizes not discriminable with eyes (spatial division), and respective color rights of R, G and B from these pixels are mixed through the simultaneously additive process to be observed as a color picture.
(2) A method of color picture display using a display apparatus as illustrated in FIG. 4 which is a schematic diagram representing a known liquid crystal display apparatus. Referring to FIG. 4, the display apparatus includes a light source 1 for emitting respective color lights of R, G and B, a liquid crystal device 3 to be illuminated with the color lights and a picture-switching means 2 for controlling the liquid crystal device 3. In picture display, the liquid crystal device 3 is illuminated sequentially (in time division) with respective color lights of R, G and B from the light source 1 while effecting light switching by the liquid crystal device 3 in synchronism with the respective color light illumination under control by the picture switching means 2. The respective color lights of R, G and B from the liquid crystal device 3 are mixed through the sequential additive process to be recognized as a color picture. This type of color display method is, e.g., disclosed in Japanese Patent Publication (JP-B) 63-41078.
Of the above-mentioned methods (1) and (2), the method (2) is advantageous in that one pixel of the liquid crystal device allows a color given by a mixture of R, G and B, thus allowing a higher resolution display.
The above-mentioned method (2) is however accompanied with the following problems (a) and (b).
(a) Motion picture blurring. This problem is explained with reference to FIG. 5A. It is assumed that a picture G moves rightward from time n to time n+1 as illustrated in FIG. 5A. If the moving picture G is followed by observation with eyes, both edge portions (hatched portions) of the moved picture are blurred due to an after image effect occurring in the eyes. A blurring of a motion picture is caused due to a restriction in eye detection speed. This problem also occurs in the method (1).
The problem has been reported in a paper entitled xe2x80x9cMotion Blurring Obstruction in Hold-Type Picture Display (in Japanese) (Collection of Papers at Electronic Communication Society, Japan, ""85/12 vol. J68-B No. 12). The paper contains a description to the effect that xe2x80x9cDetection eye speed on blurring obstruction accompanying picture motion is governed by a light emission time at a pixel.xe2x80x9d
In recent years, the blurring has been quantitatively evaluated. For example, a paper entitled xe2x80x9cStudy on Motion Picture Quality in Hold Emission-Type Display by Eight-times Accelerated CRT (in Japanese)xe2x80x9d (xe2x80x9cShin-Gaku Gihoxe2x80x9d EID 96-4 (1996-06)) contains a description to the effect that xe2x80x9cIn the hold-type, the evaluation subsides below an allowable limit at a speed of 13.6 deg/sec.xe2x80x9d
(b) Color splitting. This problem is explained with reference to FIG. 5B. It is again assumed that a color picture G moves rightward from time n to time n+1 as illustrated in FIG. 5B. If the moving color picture G is followed by observation with eyes, both edge portions (hatched portions at the display position) cause blurring of colors due to mixing of colors recognized by after image effect by eyes of a previous display before the motion with colors of a current display after the motion. This problem of color splitting is peculiar in the method (2).
The color splitting is also a problem attributable to a restriction in eye detection speed of a motion picture. This problem is discussed in, e.g., JP-B 7-41023, Japanese Laid-Open Patent Application (JP-A)8-248381, JP-A 8-317380, JP-A 8-101672 and JP-A 9-90196. (In some of these documents, a term xe2x80x9ccolor deviationxe2x80x9d is used instead of xe2x80x9ccolor splittingxe2x80x9d for an identical phenomenon.)
Several proposals have been made for solving the above-mentioned problems, but they are also accompanied with other problems as described below:
(i) For solving the problem of color splitting, JP-B 7-41023 has proposed a detection device using an electric circuit, but the proposal requires a complicated circuit and yet is unsuitable for processing a high-speed motion picture.
(ii) JP-A 8-248381 has proposed to use a succession of fields having different time orders of color signals, particularly so that the color of a final color signal in a preceding period is made identical to the color of a first color signal in a subsequent period. This however results in a lower frame frequency for the other color data, thus being liable to cause flicker.
(iii) JP-A 8-317380 has proposed a 3:1-interlaced scanning for causing different colors at an identical position on a scanning line. The use of such a special scanning scheme requires a complicated circuit system.
(iv) JP-A 8-101672 has proposed to utilize a non-chromatic color signal derived from R, G and B signals, but the preparation of such new picture data requires a complicated circuit.
(v) JP-A 9-90916 has proposed to form a sub-field of white or intermediate color of a period identical to the fields of R, G and B in addition to the R, G and B fields. The preparation of new picture data requires a complicated circuit, and the newly prepared sub-field of white or intermediate color is liable to deteriorate the picture quality.
Among the above-mentioned proposals (i) to (v), the proposals (iv) and (v) using non-chromatic picture data or white picture data are advantageous in that they are applicable to processing of high-speed motion picture without causing flicker and without utilizing a special scanning scheme. However, the preparation of new picture data to be inserted still involves a problem that the complication of circuit is inevitable.
In view of the above-mentioned circumstances of prior art, a principal object of the present invention is to provide a picture display method using a liquid crystal device capable of reducing the motion picture blurring and color splitting without requiring a complicated circuit.
According to the present invention, there is provided a color picture display method using a liquid crystal display apparatus of the type including a light source capable of emitting three primary color lights including first color light, second color light and third color light separately at arbitrary time, and a liquid crystal device for receiving and selectively switching the three primary color lights from the light source; said method comprising:
(A) illumination steps by using the light source including:
a first step of turning off the light source, and then emitting only the first color light,
a second step of turning off the light source, then emitting only the second color light, and then turning off the light source, and
a third step of emitting only the third color light and then turning off the light source, and
(B) a liquid crystal device drive step of driving the liquid crystal device for optical switching in synchronism with the illumination steps to display a picture of the first color in the first step, a picture of the second color in the second step and a picture of the third color in the third step.
In a preferred embodiment, the first to third steps have equal lengths of period, include an equal length of period for emitting the color light and include an equal length of period for turning off the light source.
As a result, a black picture is displayed at the time of turning off the light source to effectively suppress the motion picture blurring and color splitting.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.